Multimode power amplifier bias circuit with selectable bandwidth

ABSTRACT

Multimode power amplifier bias circuit with selectable bandwidth. In some embodiments, a bias circuit for a power amplifier can include a first bipolar junction transistor (BJT) configured to pass a reference current. The first BJT can be coupled with a second BJT that performs at least some amplification for the power amplifier. The first and second BJTs can be configured as a current mirror. The bias circuit can further include a coupling circuit that couples the collector and the base of the first BJT. The coupling circuit can include a switchable element to allow the coupling circuit to be in a first state or a second state. The first state can be configured to yield a first bandwidth for the bias circuit, and the second state can be configured to yield a second bandwidth for the bias circuit.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application claims priority to U.S. Provisional Application No.61/875,586 filed Sep. 9, 2013, entitled MULTIMODE POWER AMPLIFIER BIASCIRCUIT WITH SELECTABLE BANDWIDTH, the disclosure of which is herebyexpressly incorporated by reference herein in its entirety.

BACKGROUND

1. Field

The present disclosure generally relates to radio-frequency (RF)amplifiers, and more particularly, to bias circuits with selectablebandwidth.

2. Description of the Related Art

In some radio-frequency (RF) applications, wireless devices such assmart phones are configured to operate in multiple modes. Accordingly,multi-mode power amplifiers (PAs) for such wireless devices typicallyneed to support a wide variety of frequency bands and/or signalmodulation formats.

SUMMARY

According to a number of implementations, the present disclosure relatesto a bias circuit for a power amplifier. The bias circuit includes afirst bipolar junction transistor (BJT) configured to pass a referencecurrent. The first BJT is coupled with a second BJT that performs atleast some amplification for the power amplifier. The first and secondBJTs are configured as a current mirror, with each of the first andsecond BJTs having a collector, a base, and an emitter. The bias circuitfurther includes a coupling circuit that couples the collector and thebase of the first BJT. The coupling circuit includes a switchableelement to allow the coupling circuit to be in a first state or a secondstate, with the first state configured to yield a first bandwidth forthe bias circuit, and the second state configured to yield a secondbandwidth for the bias circuit.

In some embodiments, each of the first and second BJTs can be aheterojunction bipolar transistor (HBT). The first and second HBTs canbe parts of a same die.

In some embodiments, the coupling of the first and second HBTs caninclude a coupling between the base of the first HBT and the base of thesecond HBT. The coupling between the base of the first HBT and the baseof the second HBT can include a first resistance connected in serieswith a second resistance. The bias circuit can further include a bufferfield-effect transistor (FET), the buffer FET having a source, a drain,and a gate. The source and the drain of the buffer FET can couple a nodebetween the first resistance and the second resistance with a supplyvoltage VCC node. The gate of the buffer FET can be coupled to thecollector of the first HBT.

In some embodiments, the coupling circuit can include a switchableelement. The switchable element can include a switchable resistance suchthat when in the first state, a resistance associated with theswitchable resistance is part of the coupling circuit, and when in thesecond state, the resistance associated with the switchable resistanceis bypassed. The switchable resistance can include the resistanceconnected in parallel with a switch. The switch can include afield-effect transistor (FET).

In some embodiments, the switch being in the first state can result inthe bias circuit being in a low bandwidth mode. The low bandwidth modecan include a WCDMA mode. The switch being in the second state canresult in the bias circuit being in a high bandwidth mode. The highbandwidth mode can include an LTE mode.

In some embodiments, one of the first and second bandwidths cancorrespond to a bandwidth associated with WCDMA or LTE mode ofoperation. The other bandwidth can correspond to the other bandwidthassociated with WCDMA or LTE mode of operation.

In some implementations, the present disclosure relates to a method foroperating a bias circuit for a power amplifier. The method includespassing a reference current through a reference bipolar junctiontransistor (BJT) having a collector, a base, and an emitter. The methodfurther includes generating a bias current for an amplifying BJT as amirror of the reference current. The method further includes performinga switching operation between the collector and the base of thereference BJT to transition between a first state and a second state ofthe bias circuit. The first state corresponds to a first bandwidth forthe bias circuit, and the second state corresponds to a second bandwidthfor the bias circuit.

In a number of implementations, the present disclosure relates to apower amplifier die that includes a semiconductor substrate and a poweramplifier (PA) circuit formed on the semiconductor substrate. The PAcircuit includes an amplifying bipolar junction transistor (BJT) havinga collector, a base, and an emitter. The power amplifier die furtherincludes a bias circuit formed on the semiconductor substrate. The biascircuit is coupled with the PA circuit. The bias circuit includes areference BJT having a collector, a base, and an emitter. The couplingof the bias circuit and the PA circuit is configured as a currentmirror. The bias circuit further includes a switchable elementconfigured to allow the bias circuit to be in a first state or a secondstate. The first state is configured to yield a first bandwidth for thebias circuit, and the second state is configured to yield a secondbandwidth for the bias circuit.

In some embodiments, each of the amplifying BJT and the reference BJTcan be a heterojunction bipolar transistor (HBT). The semiconductorsubstrate can include a gallium arsenide (GaAs) substrate.

In accordance with a number of teachings, the present disclosure relatesto a method for fabricating a power amplifier die. The method includesproviding a semiconductor substrate. The method further includes forminga power amplifier (PA) circuit on the semiconductor substrate. The PAcircuit includes an amplifying bipolar junction transistor (BJT) havinga collector, a base, and an emitter. The method further includes forminga bias circuit on the semiconductor substrate. The bias circuit includesa reference BJT having a collector, a base, and an emitter. The biascircuit further includes a switchable element configured to allow thebias circuit to be in a first state or a second state, with the firststate configured to yield a first bandwidth for the bias circuit, andthe second state configured to yield a second bandwidth for the biascircuit. The method further includes forming a current mirror couplingbetween the bias circuit and the PA circuit.

According to a number of implementations, the present disclosure relatesto a power amplifier module that includes a packaging substrateconfigured to receive a plurality of components. The module furtherincludes a power amplifier (PA) circuit formed on a die that is mountedon the packaging substrate. The PA circuit includes an amplifyingbipolar junction transistor (BJT) having a collector, a base, and anemitter. The module further includes a bias circuit formed on the die.The bias circuit is coupled with the PA circuit. The bias circuitincludes a reference BJT having a collector, a base, and an emitter. Thecoupling of the bias circuit and the PA circuit is configured as acurrent mirror. The bias circuit further includes a switchable elementconfigured to allow the bias circuit to be in a first state or a secondstate, with the first state configured to yield a first bandwidth forthe bias circuit, and the second state configured to yield a secondbandwidth for the bias circuit. The module further includes a pluralityof connectors configured to provide electrical connections between thePA circuit, the bias circuit, and the packaging substrate.

In some implementations, the present disclosure relates to a wirelessdevice that includes a transceiver configured to process RF signals. Thewireless device further includes an antenna in communication with thetransceiver. The antenna is configured to facilitate transmission of anamplified RF signal. The wireless device further includes a poweramplifier (PA) module in communication with the transceiver. The PAmodule is configured to generate the amplified RF signal. The PA moduleincludes a PA circuit. The PA circuit includes an amplifying bipolarjunction transistor (BJT) having a collector, a base, and an emitter.The PA module further includes a bias circuit. The bias circuit iscoupled with the PA circuit. The bias circuit includes a reference BJThaving a collector, a base, and an emitter. The coupling of the biascircuit and the PA circuit is configured as a current mirror. The biascircuit further includes a switchable element configured to allow thebias circuit to be in a first state or a second state, with the firststate configured to yield a first bandwidth for the bias circuit, andthe second state configured to yield a second bandwidth for the biascircuit.

For purposes of summarizing the disclosure, certain aspects, advantagesand novel features of the inventions have been described herein. It isto be understood that not necessarily all such advantages may beachieved in accordance with any particular embodiment of the invention.Thus, the invention may be embodied or carried out in a manner thatachieves or optimizes one advantage or group of advantages as taughtherein without necessarily achieving other advantages as may be taughtor suggested herein.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 shows a block diagram of a power amplifier (PA) operatingconfiguration that includes a PA being controlled by a PA controlcomponent.

FIG. 2 shows a more specific example of the operating configuration ofFIG. 1 in an example context of a heterojunction bipolar transistor(HBT) based PA.

FIG. 3 shows an example of a bias circuit for which one or more featuresof the present disclosure can be implemented to provide switchablebandwidth selection functionality.

FIG. 4 shows an example of a PA operating configuration where a biascircuit includes a switchable component to allow the bias circuit tooperate in a plurality of modes.

FIG. 5 shows that in some embodiments, one or more switchable elementscan be implemented at one or more other parts of the example biascircuit of FIG. 4.

FIGS. 6A-6C show some non-limiting examples of how one or more circuitelements can be arranged with one or more switches to facilitateoperation of the one or more switchable elements of FIGS. 4 and 5.

FIG. 7 shows a process that can be implemented to control a bias circuithaving one or more features as described herein.

FIG. 8 shows a process that can be implemented to fabricate a biascircuit having one or more features as described herein.

FIG. 9 depicts a die that can be fabricated according to the exampleprocess of FIG. 8.

FIG. 10 depicts an example module having one or more featured asdescribed herein.

FIG. 11 depicts an example wireless device having one or moreadvantageous features described herein.

DETAILED DESCRIPTION OF SOME EMBODIMENTS

The headings provided herein, if any, are for convenience only and donot necessarily affect the scope or meaning of the claimed invention.

Many wireless devices such as smart phones are configured to operate inmultiple modes. Accordingly, multi-mode power amplifiers (PAs) for suchwireless devices typically need to support a wide variety of frequencybands and/or signal modulation formats. For example, in a typical hybridPA architecture, a given amplifier chain is used to boost both WCDMA(3G) and LTE (4G) signals. While output power, frequency, and gainrequirements might be similar, demands on bias circuitry for such anamplifier chain can be quite different.

By way of examples, for WCDMA operation, stringent noise requirements atfrequency offsets as close as 45 MHz from a carrier frequency can beimposed to prevent degrading the sensitivity of a receiver. Accordingly,bias bandwidth can be set at around 20 MHz or lower to minimize orreduce bias noise contribution to the overall PA noise.

For LTE operation, bias bandwidth needs to be wide enough to support,for example, 20 MHz/100 RB signals without generating memory effectswhich degrade adjacent channel power. Accordingly, bias bandwidth thatis wider than 60 MHz is typically needed.

In some conventional bias circuit designs, an emitter follower can beused with its base biased 2 VBE above ground to provide a correspondingbase current into the power amplifier. Such a circuit can provide bothlow noise and consistent output impedance for the widest LTE modulationbandwidth. However, a drawback of such a circuit is that the circuitrequires significant voltage headroom for proper operation. In thecontext of a gallium arsenide (GaAs) heterojunction bipolar transistor(HBT) power amplifier design, a minimum supply voltage typically needsto be approximately 3.0V or greater for this circuit to be effective.However, such a voltage is typically higher than the minimum batteryvoltages specified in many wireless handset designs.

In some conventional bias circuit designs, a current mirror bias circuitwith field-effect transistor (FET) buffer is commonly used to extend thebattery voltage down to, for example, approximately 2.5V. In order toremove the FET's VGS variation due to effects such as temperature,process, and output current, such a current mirror bias circuit istypically used in a feedback circuit. Such a feedback circuit can imposea bandwidth constraint. PA performance parameters such as outputimpedance (which is related to PA linearity) and noise rejection canconflict with such a constraint in the bias circuit bandwidth.

Disclosed herein are various examples of circuits, devices and methodsthat can be configured to, among others, address the foregoingchallenges associated with PAs and their bias circuits. In someimplementations as described herein, a current mirror bias circuit witha FET buffer can be configured to support operation of, for example, anHBT power amplifier at battery voltages below, for example,approximately 3.0V. In the example contexts of WCDMA and LTE, arelatively low bias bandwidth is desired for WCDMA, and a relativelyhigh bias bandwidth is desired for LTE. For such examples, a currentmirror bias circuit can be configured to include a feature of selectablebandwidth.

FIG. 1 schematically shows a PA operating configuration 100 thatincludes a PA 102 being controlled (line 106) by a PA control component104. FIG. 2 shows a more specific example of such an operatingconfiguration 100 in an example context of an HBT 110 based PA. Althoughdescribed herein in such a context, it will be understood that one ormore features of the present disclosure can also be implemented in PAsbased on other types of transistors.

In FIG. 2, a radio-frequency (RF) signal being amplified can be providedto the base of the HBT 110 from an input port (RF_in). Such an inputsignal can be passed through an input path that can include, forexample, a matching network (not shown) and a DC-block capacitance (notshown). The amplified signal can then be output through the collector ofthe HBT 110, and then through an output port (RF_out). In the example ofFIG. 2, supply voltage VCC can be provided to the collector of the HBT110.

As further shown in FIG. 2, a PA control component 104 can include abias circuit 114. The bias circuit 114 is shown to be coupled to thebase of the HBT 110. Various examples of the bias circuit 114 aredescribed herein in greater detail.

FIG. 3 shows an example of a bias circuit 14 for which one or morefeatures of the present disclosure can be implemented to provideswitchable bandwidth selection functionality. The example bias circuit14 is shown to provide a bias signal to an amplifier circuit 10. In someembodiments, the amplifier circuit 10 can be one of a plurality ofamplification stages of an amplifier, including but not limited to adriver stage.

The example amplifier circuit 10 is shown to include a bipolartransistor Q2 such as an HBT having a base, an emitter, and a collector.The emitter can be coupled to, for example, a ground. The base is shownto be coupled to a node 54 which is in communication with an input node(RF_in) for receiving an RF signal to be amplified. The collector isshown to be coupled to a node 50 which is in communication with anoutput node (RF_out) for outputting the amplified RF signal.

In the example of FIG. 3, supply voltage VCC is shown to be provided tothe collector of the transistor Q2 through a line element 52. In someembodiments, the line element 52 can be, for example, a chokeinductance.

In the example of FIG. 3, the bias circuit 14 is shown to provide adesired bias current to the transistor Q2 by a current mirrorconfiguration between a reference transistor Q1 and the amplifyingtransistor Q2. In the example mirror configuration, the base of Q1 andthe base of Q2 are shown to be coupled through resistances 74 and 76.

On the reference side, a reference current generator is shown togenerate Iref from a supply voltage VCC, and Iref is shown to beprovided to the collector of the transistor Q1. In some embodiments,both of the transistors Q1 and Q2 can be formed on the same die so as toallow their device properties (e.g., beta values) to be substantiallymatched. Such matching of the transistors Q1 and Q2 can allow the outputcurrent of the mirror (collector current of Q2) to be proportional tothe collector current (Iref) of Q1.

In the example shown in FIG. 3, the bandwidth of a feedback loopassociated with the current mirror bias circuit 14 can be determined atleast in part by a collector-base coupling circuit between the collector(e.g., at node 62) and the base (e.g., at node 68) of Q1. The examplecollector-base coupling circuit is shown to include a capacitance C1connected in series with a resistance 72.

In the example shown in FIG. 3, buffer functionality can be provided bya FET (FET1) whose source/drain terminals couple the supply voltage VCCto node 70 between the bases of Q1 and Q2. The gate of FET1 is shown tobe coupled to the output of the Iref generator (at node 60).

FIG. 4 shows an example of a PA operating configuration 100, where abias circuit 114 includes a switchable component to allow the biascircuit 114 to operate in a plurality of modes. In various examplesdescribed herein, such modes can include WCDMA (where a relatively lowbias bandwidth is desired) and LTE (where a relatively high biasbandwidth is desired). Although described in the context of such examplemodes, it will be understood that one of more features of the presentdisclosure can also be implemented for other modes of operation.

In the example configuration 100 of FIG. 4, an amplifier circuit 110 canbe similar to the example amplifier circuit 10 of FIG. 3. Moreparticularly, the amplifier circuit 110 can include a bipolar transistorQ2 such as an HBT having a base, an emitter, and a collector. Theemitter can be coupled to a ground. The base is shown to be coupled to anode 154 which is in communication with an input node (RF_in) forreceiving an RF signal to be amplified. The collector is shown to becoupled to a node 150 which is in communication with an output node(RF_out) for outputting the amplified RF signal. A supply voltage VCC isshown to be provided to the collector of the transistor Q2 through aline element 152 (e.g., a choke inductance).

In the example configuration 100 of FIG. 4, parts of a bias circuit 114can be similar to the example of FIG. 3. More particularly, the biascircuit 114 can be configured to provide a desired bias current to thetransistor Q2 by a current mirror configuration between a referencetransistor Q1 and the amplifying transistor Q2. In the example mirrorconfiguration, the base of Q1 and the base of Q2 are shown to be coupledthrough resistances R3 and R4.

On the reference side, a reference current generator is shown togenerate Iref from a supply voltage VCC, and Iref is shown to beprovided to the collector of the transistor Q1. In some embodiments,both of the transistors Q1 and Q2 can be formed on the same die so as toallow their device properties (e.g., beta values) to be substantiallymatched. Such matching of the transistors Q1 and Q2 can allow the outputcurrent of the mirror (collector current of Q2) to be proportional tothe collector current (Iref) of Q1.

In the example shown in FIG. 4, buffer functionality can be provided bya FET (FET1) whose source/drain terminals couple the supply voltage VCCto node 170 between the bases of Q1 and Q2. The gate of FET1 is shown tobe coupled to the output of the Iref generator (at node 160).

In the example shown in FIG. 4, the bandwidth of a feedback loopassociated with the current mirror bias circuit 114 can be determined atleast in part by a collector-base coupling circuit between the collector(e.g., at node 162) and the base (e.g., at node 168) of Q1. The examplecollector-base coupling circuit is shown to include a series connectionof a capacitance C1, a resistance R1, and a switchable element 200. Forexample, the switchable element 200 can include a resistance R2connected in parallel with a FET (FET2) between nodes 164 and 168, withthe node 164 being between R1 and R2.

The switchable element 200 being configured in the foregoing examplemanner can allow the RC value of the collector-base coupling circuit forQ1 to change between two values. Such a change can be implemented byswitching FET2 between OFF and ON states with a control signal V_CTLapplied to its gate. When FET2 is in the ON state, R2 can be bypassed,so that the RC value is approximately R1×C1. When FET2 is in the OFFstate, the RC value is approximately (R1−FR2)×C1. In the example contextof WCDMA and LTE operations, FET2 can be turned ON to yield an LTE orhigh bandwidth mode; and FET2 can be turned OFF to yield a WCDMA or lowbandwidth mode.

FIG. 5 shows that in some embodiments, one or more switchable elementscan be implemented at other parts of a bias circuit. For the purpose ofdescription of an example configuration 100 of FIG. 5, it will beassumed that an amplifier circuit 110 and its coupling to node 170 canbe similar to the example of FIG. 4. Similarly, coupling of a buffer FET(FET1) between VCC and node 170, coupling of Iref (with VCC input) andQ1, and collector-base coupling (that includes a switchable element 200)for Q1, can be similar to the examples described in reference to FIG. 4.

In the example configuration 100 of FIG. 5, two additional switchableelements 200′, 200″ are shown to be implemented. The switchable element200′ is shown to be implemented between the gate of FET1 and node 160which is between the Iref generator and the collector of Q1. Theswitchable element 200′ is shown to include a resistance R5 connected inparallel with a FET (FET3) between nodes 180 (connected to node 160) and182 (connected to the gate of FET1). FET3 is shown to be provided with acontrol signal V_CTL to thereby allow it to be in an ON or an OFF state,so as to allow insertion (FET3 OFF) or removal (FET3 ON) of resistanceR5 between the gate of FET1 and node 160.

The switchable element 200″ is shown to be implemented between the gateof FET1 and signal ground. The switchable element 200″ is shown toinclude a resistance R6 connected in parallel with a FET (FET4) betweennode 186 (connected to node 184 and the gate of FET1) and 188 (connectedto the signal ground through a capacitance C2). FET4 is shown to beprovided with a control signal V_CTL to thereby allow it to be in an ONor an OFF state, so as to allow insertion (FET4 OFF) or removal (FET4ON) of resistance R6 in the RC coupling between the gate of FET1 and thesignal ground.

In some embodiments, the example switches FET2, FET3, FET4 can becontrolled by a common V_CTL signal. Such a V_CTL applied to FET2 canallow the current mirror bias circuit 114 to operate in low or highbandwidth mode. By switching the additional example devices FET3, FET4,one or more additional changes in the bandwidth of the bias feedbackloop. For example, in the low bandwidth mode, the additional switchesFET3, FET4 and their respective switched components R5, R6 can beconfigured to insert one or more poles in the feedback loop to, forexample, further attenuate noise at a selected frequency while stillsubstantially maintaining the desired bandwidth of the bias circuit 114.

In the various examples of switchable elements in FIGS. 4 and 5, aresistance is described as being in parallel with a FET. It will beunderstood that other configurations can also be implemented utilizingdifferent switches, different circuit elements, and/or differentarrangements of such switches and circuit elements.

FIGS. 6A-6C show some non-limiting examples of how one or more circuitelements 204, 214 (e.g., resistance, capacitance, inductance, etc.) canbe arranged with one or more switches 202, 212. For example, FIG. 6Ashows a configuration 201 having a switch S (202) in parallel with acircuit element 204, between nodes 206, 208. Such a configuration can besimilar to the examples described in reference to FIGS. 4 and 5, wherethe switch S is a FET, and the circuit element is a resistance.

In another example, FIG. 6B shows a configuration 201′ having a switch S(202) in series with a circuit element 204, between nodes 206, 208. Inyet another example, FIG. 6C shows a configuration 201″ having twoin-series circuits (51 (202) in series with a circuit element 204, andS2 (212) in series with a circuit element 214) connected in parallelbetween nodes 206, 208. Other configurations of circuit element(s) andswitch(es) can also be implemented.

FIG. 7 shows a process 300 that can be implemented to control a biascircuit having one or more features as described herein. In block 302, asignal indicating a mode of operation of a power amplifier can beobtained. In block 304, a switching operation can be performed in thebias circuit to yield a desired output of the bias circuit for the poweramplifier.

FIG. 8 shows a process 350 that can be implemented to fabricate a biascircuit having one or more features as described herein. In block 352, apower amplifier circuit can be formed on a semiconductor die. In block354, a bias circuit can be formed on the same semiconductor die. Thebias circuit can include a switchable element to allow switching betweenfirst and second modes of the bias circuit for the power amplifiercircuit. In block 356, one or more electrical connections can be formedbetween the bias circuit and the power amplifier circuit.

FIG. 9 schematically depicts a die 400 that can be fabricated accordingto the example process 350 of FIG. 8. The semiconductor die 400 caninclude a substrate 402, and a power amplifier (PA) circuit 110 (e.g.,HBT) can be formed on the substrate 402. A bias circuit 114 can also beformed on the substrate 402. For example, and in the context of an HBTPA, at least an HBT of the bias circuit for a current mirror can beformed on the same substrate 402. A plurality of connection pads 404 canalso be formed on the substrate 402 to provide, for example, power andsignals for the PA circuit 102 and the bias circuit 114.

In some implementations, one or more features described herein can beincluded in a module. FIG. 10 schematically depicts an example module450 having a packaging substrate 452 that is configured to receive aplurality of components. In some embodiments, such components caninclude a die 400 having one or more featured as described herein. Forexample, the die 400 can include a PA circuit 102 and a bias circuit114. A plurality of connection pads 404 can facilitate electricalconnections such as wirebonds 454 to connection pads 456 on thesubstrate 452 to facilitate passing of various power and signals to andfrom the die 400.

In some embodiments, other components can be mounted on or formed on thepackaging substrate 452. For example, one or more surface mount devices(SMDs) (460) and one or more matching networks (462) can be implemented.In some embodiments, the packaging substrate 452 can include a laminatesubstrate.

In some embodiments, the module 450 can also include one or morepackaging structures to, for example, provide protection and facilitateeasier handling of the module 450. Such a packaging structure caninclude an overmold formed over the packaging substrate 452 anddimensioned to substantially encapsulate the various circuits andcomponents thereon.

It will be understood that although the module 450 is described in thecontext of wirebond-based electrical connections, one or more featuresof the present disclosure can also be implemented in other packagingconfigurations, including flip-chip configurations.

In some implementations, a device and/or a circuit having one or morefeatures described herein can be included in an RF device such as awireless device. Such a device and/or a circuit can be implementeddirectly in the wireless device, in a modular form as described herein,or in some combination thereof. In some embodiments, such a wirelessdevice can include, for example, a cellular phone, a smart-phone, ahand-held wireless device with or without phone functionality, awireless tablet, a wireless router, a wireless access point, a wirelessbase station, etc.

FIG. 11 schematically depicts an example wireless device 500 having oneor more advantageous features described herein. One or more PAs 110 asdescribed herein are shown to be biased by one or more bias circuit 114having one or more features as described herein. In embodiments wherethe PAs 110 and their bias circuit(s) 114 are packaged into a module,such a module can be represented by a dashed box 450. In someembodiments, the module 450 can include at least some of input andoutput matching circuits 112, 206.

The PAs 110 can receive their respective RF signals from a transceiver510 that can be configured and operated in known manners to generate RFsignals to be amplified and transmitted, and to process receivedsignals. The transceiver 510 is shown to interact with a basebandsub-system 508 that is configured to provide conversion between dataand/or voice signals suitable for a user and RF signals suitable for thetransceiver 510. The transceiver 510 is also shown to be connected to apower management component 506 that is configured to manage power forthe operation of the wireless device 500. Such power management can alsocontrol operations of the baseband sub-system 508 and the module 450.

The baseband sub-system 508 is shown to be connected to a user interface502 to facilitate various input and output of voice and/or data providedto and received from the user. The baseband sub-system 508 can also beconnected to a memory 504 that is configured to store data and/orinstructions to facilitate the operation of the wireless device, and/orto provide storage of information for the user.

In the example wireless device 500, outputs of the PAs 110 are shown tobe matched and routed to an antenna 516 via their respective duplexers512 a-512 d and a band-selection switch 514. The band-selection switch514 can be configured to allow selection of, for example, an operatingband or an operating mode. In some embodiments, each duplexer 512 canallow transmit and receive operations to be performed simultaneouslyusing a common antenna (e.g., 516). In FIG. 11, received signals areshown to be routed to “Rx” paths (not shown) that can include, forexample, a low-noise amplifier (LNA).

Unless the context clearly requires otherwise, throughout thedescription and the claims, the words “comprise,” “comprising,” and thelike are to be construed in an inclusive sense, as opposed to anexclusive or exhaustive sense; that is to say, in the sense of“including, but not limited to.” The word “coupled”, as generally usedherein, refers to two or more elements that may be either directlyconnected, or connected by way of one or more intermediate elements.Additionally, the words “herein,” “above,” “below,” and words of similarimport, when used in this application, shall refer to this applicationas a whole and not to any particular portions of this application. Wherethe context permits, words in the above Detailed Description using thesingular or plural number may also include the plural or singular numberrespectively. The word “or” in reference to a list of two or more items,that word covers all of the following interpretations of the word: anyof the items in the list, all of the items in the list, and anycombination of the items in the list.

The above detailed description of embodiments of the invention is notintended to be exhaustive or to limit the invention to the precise formdisclosed above. While specific embodiments of, and examples for, theinvention are described above for illustrative purposes, variousequivalent modifications are possible within the scope of the invention,as those skilled in the relevant art will recognize. For example, whileprocesses or blocks are presented in a given order, alternativeembodiments may perform routines having steps, or employ systems havingblocks, in a different order, and some processes or blocks may bedeleted, moved, added, subdivided, combined, and/or modified. Each ofthese processes or blocks may be implemented in a variety of differentways. Also, while processes or blocks are at times shown as beingperformed in series, these processes or blocks may instead be performedin parallel, or may be performed at different times.

The teachings of the invention provided herein can be applied to othersystems, not necessarily the system described above. The elements andacts of the various embodiments described above can be combined toprovide further embodiments.

While some embodiments of the inventions have been described, theseembodiments have been presented by way of example only, and are notintended to limit the scope of the disclosure. Indeed, the novel methodsand systems described herein may be embodied in a variety of otherforms; furthermore, various omissions, substitutions and changes in theform of the methods and systems described herein may be made withoutdeparting from the spirit of the disclosure. The accompanying claims andtheir equivalents are intended to cover such forms or modifications aswould fall within the scope and spirit of the disclosure.

What is claimed is:
 1. A bias circuit for a power amplifier, the biascircuit comprising: a first bipolar junction transistor (BJT) configuredto pass a reference current, the first BJT coupled with a second BJTthat performs at least some amplification for the power amplifier, thefirst and second BJTs configured as a current mirror, each of the firstand second BJTs having a collector, a base, and an emitter; and acoupling circuit that couples the collector and the base of the firstBJT, the coupling circuit including a switchable element to allow thecoupling circuit to be in a first state or a second state, the firststate configured to yield a first bandwidth for the bias circuit, thesecond state configured to yield a second bandwidth for the biascircuit.
 2. The circuit of claim 1 wherein each of the first and secondBJTs is a heterojunction bipolar transistor (HBT).
 3. The circuit ofclaim 2 wherein the first and second HBTs are parts of a same die. 4.The circuit of claim 2 wherein the coupling of the first and second HBTsincludes a coupling between the base of the first HBT and the base ofthe second HBT.
 5. The circuit of claim 4 wherein the coupling betweenthe base of the first HBT and the base of the second HBT includes afirst resistance connected in series with a second resistance.
 6. Thecircuit of claim 5 further comprising a buffer field-effect transistor(FET), the buffer FET having a source, a drain, and a gate.
 7. Thecircuit of claim 6 wherein the source and the drain of the buffer FETcouple a node between the first resistance and the second resistancewith a supply voltage VCC node.
 8. The circuit of claim 7 wherein thegate of the buffer FET is coupled to the collector of the first HBT. 9.The circuit of claim 2 wherein the coupling circuit includes aswitchable element.
 10. The circuit of claim 9 wherein the switchableelement includes a switchable resistance such that when in the firststate, a resistance associated with the switchable resistance is part ofthe coupling circuit, and when in the second state, the resistanceassociated with the switchable resistance is bypassed.
 11. The circuitof claim 10 wherein the switchable resistance includes the resistanceconnected in parallel with a switch.
 12. The circuit of claim 11 whereinthe switch includes a field-effect transistor (FET).
 13. The circuit ofclaim 11 wherein the switch being in the first state results in the biascircuit being in a low bandwidth mode.
 14. The circuit of claim 13wherein the low bandwidth mode includes a WCDMA mode.
 15. The circuit ofclaim 11 wherein the switch being in the second state results in thebias circuit being in a high bandwidth mode.
 16. The circuit of claim 15wherein the high bandwidth mode includes an LTE mode.
 17. A poweramplifier die comprising: a semiconductor substrate; a power amplifier(PA) circuit formed on the semiconductor substrate, the PA circuitincluding an amplifying bipolar junction transistor (BJT) having acollector, a base, and an emitter; and a bias circuit formed on thesemiconductor substrate, the bias circuit coupled with the PA circuit,the bias circuit including a reference BJT having a collector, a base,and an emitter, the coupling of the bias circuit and the PA circuitconfigured as a current mirror, the bias circuit further including aswitchable element configured to allow the bias circuit to be in a firststate or a second state, the first state configured to yield a firstbandwidth for the bias circuit, the second state configured to yield asecond bandwidth for the bias circuit.
 18. The power amplifier die ofclaim 17 wherein each of the amplifying BJT and the reference BJT is aheterojunction bipolar transistor (HBT).
 19. The power amplifier die ofclaim 18 wherein the semiconductor substrate includes a gallium arsenide(GaAs) substrate.
 20. A wireless device comprising: a transceiverconfigured to process RF signals; an antenna in communication with thetransceiver, the antenna configured to facilitate transmission of anamplified RF signal; and a power amplifier (PA) module in communicationwith the transceiver and configured to generate the amplified RF signal,the PA module including a PA circuit, the PA circuit including anamplifying bipolar junction transistor (BJT) having a collector, a base,and an emitter, the PA module further including a bias circuit, the biascircuit coupled with the PA circuit, the bias circuit including areference BJT having a collector, a base, and an emitter, the couplingof the bias circuit and the PA circuit configured as a current mirror,the bias circuit further including a switchable element configured toallow the bias circuit to be in a first state or a second state, thefirst state configured to yield a first bandwidth for the bias circuit,the second state configured to yield a second bandwidth for the biascircuit.